1. Field of the Invention
The present invention relates to an adhesive composition having thermosetting properties, and a heat resistant adhesive film which is obtained by using the adhesive composition and does not curl easily, and a wiring film using the adhesive composition.
2. Background of the Invention
In recent years, electronic devices have been decreased in size, thickness, and weight and wiring members used therefor have been required to realize multilayer wirings, fine wirings, and thinning in order to satisfy high-density fine wiring. Further, lead free solder has been used progressively in the relevant field with the aim of decreasing environmental burdens. Under such situations, wiring members such as FFC (flexible flat cable), TAB (tape automated bonding) tape, FPC (flexible printed circuit) and MFJ (multi-frame joiner) are required to have improved heat resistance.
An insulating layer for the above-mentioned wiring members are basically composed of a base film and an adhesive layer. Such a wiring member is described, for example, in Japanese Patent Laid-Open No. Hei 05-29399 (Patent Document 1), in which the base film used therein is, for example, an organic insulating film composed of a heat resistant film such as polyimide, polyether imide, polyphenylene sulfide or polyether ether ketone, or a composite heat resistant film such as epoxy resin-glass cloth or epoxy resin-polyimide-glass cloth. Patent Document 1 discloses use of an adhesive composition containing a polyamide resin and an epoxy resin as the adhesive layer.
However, the adhesive composition described in Patent Document 1 has a problem in storage stability of the heat resistant adhesive film due to high reactivity between the amino group present in the polyamide resin structure and the epoxy resin. For overcoming this problem, Japanese Patent Laid-Open No. 2004-136631 (Patent Document 2) proposes an adhesive composition composed of a phenoxy resin having at both ends thereof an epoxy group, an acrylic rubber, and a curing agent. As the phenoxy resin, a bisphenol A type, a bisphenol F type, a bisphenol AD type, a bisphenol S type, and a copolymerization type having bisphenol A and bisphenol F are exemplified.
Japanese Patent Laid-Open No. 2010-150437 (Patent Document 3) discloses an adhesive composition containing a thermoplastic polyurethane resin having a weight-average molecular weight of from 80,000 to 800,000, an epoxy resin, and an epoxy resin curing agent, in order to overcome the above-mentioned problems.
Since a typical polyurethane resin has high reactivity with an epoxy resin, an adhesive film using it has a problem in storage stability. Patent Document 3 describes that an adhesive film using a polyurethane resin with a molecular weight within a predetermined range has improved storage stability. It has adhesive force of from 1.1 kN/m to 1.7 kN/m.
Japanese Patent Laid-Open No. 2010-143988 (Patent Document 4) discloses that an adhesive composition containing a polyurethane resin, an epoxy resin, and a novolac resin with a specific structure has solder heat resistance of 300° C.
Japanese Patent Laid-Open No. 2001-262111 (Patent Document 5) discloses an adhesive composition containing a (meth)acryl-modified phenoxy resin and an epoxy resin and Japanese Patent Laid-Open No. 2008-258607 (Patent Document 6) discloses an adhesive composition containing a (meth)acryl-modified phenoxy resin, a urethane acrylate oligomer and a silane coupling agent. The epoxy-containing adhesive composition described in Patent Document 5 has excellent heat resistance. The adhesive composition containing a urethane acrylate and a silane coupling agent described in Patent Document 6 has an excellent adhesive force with a metal conductor.
In addition, it is important that the adhesive film using the adhesive composition is resistant to curl as much as possible from the standpoint of the handling properties of the adhesive film.